Large screen display images, such as those provided by contemporary large screen televisions and large computer monitors, are popular for a number of reasons. One reason for large screen image appeal is the ability to present more detail and a larger apparent field of view (FOV). However, the large FOV image generally comes with a tradeoff against space; large screen display systems typically require a big spatial footprint for accommodating the required amount of display electronics, drive electronics, and the plurality of imaging optics necessary to produce the large screen image. Examples of such imaging optics can include an array of electro-optic pixels such as an active matrix LCD or OLED panel for direct viewing, or a projector and screen for large screen projection.
The distance between the pupil of the viewer and the output surface of the imaging optics of a display system is referred to as the “eye relief.” The range of valid locations from which a viewer views an image can be referred to as an eye box. In addition to occupying a big spatial footprint, display systems optimized to generate large FOV images are typically characterized by having a large eye relief and a large eye box. Overall, display system applications span a wide range of eye relief and eye box requirements; for example, from centimeters for a near-to-eye (NTE) display, to multiple meters for a large screen television.
There are several significant display system applications characterized by “mid-range” eye relief and eye box requirements. Examples of such “mid-range display systems” include: head up display systems (HUDs); display systems for instruments such as hand-held devices, medical equipment and portable test equipment; automotive applications; and personal media players. Compared to displays mounted in a fixed relationship to the viewer's head, mid-range display systems typically require a more flexible range of eye relief distance and a larger eye box. As each of these mid-range applications evolves, there is an increasing design expectation that the optical performance of those display systems shall provide high quality, high resolution, full color, and large FOV images. However, traditional large screen display systems typically cannot provide the combination of optical performance and flexibility that mid-range applications require, while keeping within the available space/volume for the hardware.
In response to the foregoing, a compact display system and method for creating a high quality, high spatial frequency, large FOV virtual image at a mid-range eye relief, while occupying minimal volume is desirable. The desirable compact display (i) enables a flexible range of eye relief, and (ii) enables a large eye box.